Abstract: A polyolefin porous material is produced by synthesizing silica particles, polysiloxane particles or crosslinked vinyl polymer particles having an average particle diameter of 0.01 to 0.1 &mgr;m in a molten polyolefin to obtain a polyolefin composition. The polyolefin composition is subsequently subjected to molding and stretching to obtain a polyolefin porous material. The obtained polyolefin porous material contains fine particles dispersed therein, substantially without forming agglomerates, and has an average pore diameter of 0.005 to 0.1 &mgr;m. The small pore diameter allows the material to be used as a liquid/liquid separation membrane, a base material for precision filtration, or a separator for batteries.

Abstract: Disclosed is a microporous shaped polyolefin article comprising a polyolefin and synthetic resin particles dispersed therein and having a softening temperature or a decomposition temperature higher than the shaping temperature of the polyolefin resin, said article having a network structure composed of open-cellular pores with a maximum pore diameter of not more than 5 micromoters, having a porosity of 20 to 90% and being molecularly oriented by stretching. A process for its production is also provided.

Abstract: Disclosed is a microporous polyproplene film comprising a propylene homopolymer, a copolymer of propylene with other copolymerizable monomer or a blend thereof, which has an intrinsic viscosity (.eta.) of 1.9 to 3.0 dl/g, especially 2.0 to 3.0 dl/g, as measured at 135.degree. C. in tetralin, said microporous film having a network structure comprising intercommunicating pores having a maximum pore size smaller than 1.mu. and an average pore size of 0.005 to 0.6.mu. and having a porosity of 30 to 90%, an air permeability of 5 to 500 sec/100 cc and a thickness of 5 to 200.mu., said microporous film being molecularly oriented by stretching.